The invention relates to an adjusting apparatus for a pneumatically actuated disc brake.
Pneumatically actuated disc brakes have, presently, become standard in heavy commercial vehicles.
The disc brake, as a rule, is assigned a pneumatically actuated brake cylinder having a piston rod, which acts on an application device for the disc brake in order to apply the brake. Known types of construction are the sliding-caliper disc brake, the hinged-caliper disc brake, and the fixed caliper disc brake.
Disc brakes of this type require a mechanical step-up (force-multiplier) in order to generate the required application force, since the force of the pneumatically loaded brake cylinder is restricted on account of the pressure level (at the present time, approximately 10 bar) and the limited overall size of the brake cylinders.
In the pneumatically actuated disc brakes known at the present time, step-up ratios of between 10:1 and 20:1 are found. The piston strokes of the brake cylinders range between 50 and 70 mm, thus resulting in an application travel of about 4 mm in order to press the brake lining onto the brake disc.
The frictional material thickness of the brake linings usually lies in the region of 20 mm. Since two linings are installed, this results, not taking into account the disc wear, in a wear travel of about 40 mm. This wear travel is greater by a multiple than the actual application travel for applying the brake. There is therefore the need to adjust the brake according to the lining wear by way of a wear adjusting apparatus.
The state of the art provides an automatically operating wear adjustment, which ensures that what is known as the lift play, that is to say the gap between the brake linings and the brake disc in the unactuated state, is kept constant independently of the state of wear and the wear behavior of the brake linings.
In one type of construction of known disc brakes, adjusting apparatuses are accommodated concentrically in the cavity of a threaded spindle and are driven eccentrically by the brake lever via a drive element (shift finger) (see, for example, DE 19 729 024 C1 or EP 0 566 008 A1 or WO 91/19115).
During braking actions, the brake lever coupled to the piston rod of the brake cylinder executes a rotational movement. Before the rotational movement of the lever is introduced into the adjuster via the coupling mechanism for adjustment (shift fork and shift finger), an idle travel, as it is known, has to be overcome. This travel is critical for the size of the lift play, since, during this movement, adjustment is not activated and the application travel then constitutes the lift play.
After the idle travel has been overcome, the adjuster is set in rotational movement, an adjusting operation being initiated as a result of coupling to the threaded spindle.
A basic component of the wear adjuster is the unidirectional coupling, which may be designed, for example, as a clamping roller freewheel. What is achieved by this free wheel, occasionally also designated as a unidirectional coupling, is that the adjuster can be rotated by the brake lever in the feed direction only and is not reset (left-hand side in FIG. 1). Having a rolling-body coupling in an unidirectional coupling is known from WO 91/19115 (FIG. 3). However, this arrangement is still relatively costly and is to be improved further in terms of its operating reliability.
A clamping roller freewheel is a precision component, which requires a high accuracy of the corresponding components for satisfactory functioning. The high accuracy of the operating elements results in a relatively high outlay in terms of cost for producing the components.
The present invention provides a wear adjusting apparatus with which the production costs are reduced while operational reliability continues to be good.
According to the invention, a wear adjusting apparatus is provided for a pneumatically actuated disc brake, in particular for arrangement in a rotatable spindle of the disc brake, having an overload coupling and an unidirectional coupling. The unidirectional coupling has a rolling-body coupling and friction clutches, which are arranged on both sides of the rolling-body coupling.
Advantageous refinements are described and claimed herein.
According to the invention, the unidirectional coupling is implemented with the requirement of only a low outlay in terms of production costs, without this being accompanied by a restriction in functioning or an increase in overall space.
An inventive disc brake is also provided which incorporates the wear adjusting apparatus according to the invention.
In summary, the following advantages arise:                simple construction;        lower accuracy requirements to be met by the individual parts;        low tolerance sensitivity;        production of the components by non-cutting forming;        high adaptability owing to diverse parameter setting possibilities;        settable moment of friction in the “overrun direction” by use of a torsion spring; and        low operating hysteresis, since all the movable parts are mounted on ball bearings.        